1. Field of the Invention
This invention relates to a nozzle that discharges droplets of a processing liquid for processing substrate, a substrate processing apparatus that includes the nozzle, and a substrate processing method that uses the nozzle. Examples of substrates to be processed include semiconductor wafers, substrates for liquid crystal displays, substrates for plasma displays, substrates for FEDs (Field Emission Displays), substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photomasks, ceramic substrates, substrates for solar cells, etc.
2. Description of Related Art
In a production process of a semiconductor device or a liquid crystal display device, etc., a cleaning process is performed to remove particles and other foreign substances from a substrate, such as a semiconductor wafer, a glass substrate for liquid crystal display device, etc. For example, each of Japanese Unexamined Patent Application Publication No. 2007-227878 and Japanese Unexamined Patent Application Publication No. 2010-56376 discloses a substrate processing apparatus of the single-substrate treatment type that cleans a substrate by making droplets of a processing liquid collide against the substrate.
The substrate processing apparatus described in Japanese Unexamined Patent Application Publication No. 2007-227878 includes a two-fluid nozzle that forms droplets of a processing liquid by making the processing liquid collide with a gas. The two-fluid nozzle includes a casing in which a processing liquid discharge port and a gas discharge port are formed. When the processing liquid and the gas are discharged at the same time from the processing liquid discharge port and the gas discharge port, respectively, the processing liquid and the gas collide in a vicinity of the casing, and droplets of the processing liquid are thereby formed.
The substrate processing apparatus described in Japanese Unexamined Patent Application Publication No. 2010-56376 includes a cleaning nozzle that forms droplets of the processing liquid by applying vibration to the processing liquid. The cleaning nozzle includes a tubular body having a plurality of discharge ports formed therein and a piezo element mounted to the tubular body. The processing liquid is supplied at a pressure of no more than 10 MPa to an interior of the tubular body. When an AC voltage is applied to the piezo element, vibration is applied to the processing liquid inside the tubular body and droplets of the processing liquid are sprayed from the plurality of discharge ports.
In cleaning a substrate by making droplets of a processing liquid collide against the substrate, it is preferable for a large number of the droplets to be sprayed from a nozzle. That is, the greater a number of times of collision of droplets against the substrate, the higher a probability of collision against foreign substances attached to the substrate and the higher a removal effect, and satisfactory cleaning can thus be performed when the number of droplets sprayed from the nozzle is large. Further, with a larger number of droplets, the same cleaning process can be performed in a shorter time and thus a number of substrates processed per time can be increased. Also, in cleaning a substrate by making droplets of the processing liquid collide against the substrate, it is preferable for a variation in size (particle diameter) of droplets and a variation in speed of the droplets to be small. That is, when the variation in particle diameter and/or the variation in speed are or is large, non-uniformity of cleaning may occur or a device pattern formed on the substrate may become damaged and the device pattern may become destroyed.
With the two-fluid nozzle described above, the droplets of the processing liquid are formed by making the processing liquid and the gas collide. It is thus difficult to control the particle diameter and the speed. On the other hand, with the cleaning nozzle described in Japanese Unexamined Patent Application Publication No. 2010-56376, the variation of particle diameter and the variation of speed can be suppressed by controlling the pressure of the processing liquid supplied to the cleaning nozzle and the vibration of the piezo element. Satisfactory cleaning can thus be performed.
However, with the cleaning nozzle described in Japanese Unexamined Patent Application Publication No. 2010-56376, a high pressure is required to spray droplets of high speed from small holes and thus the processing liquid is supplied to the interior of the tubular body at a pressure of 10 MPa at the maximum. Thus, for example, a tubular body with adequate thickness must be used to secure strength enabling withstanding of the liquid pressure in the cleaning nozzle. However, if the thickness of the tubular body is large, the cleaning nozzle is made large. The cleaning nozzle is installed in a limited space inside the substrate processing apparatus and is thus preferably compact.